Device for determining the quantity of water required by a cultivation medium, and a plant tray adapted to implementing the device

ABSTRACT

The device for determining the quantity of water required by a cultivation medium placed in a tray (100), comprises a vertically disposed measuring wheel (10) mounted on a vertical partition (106) in such a manner as to be free to rotate about a horizontal axis (19), while being unbalanced. The bottom portion of the measuring wheel (10) is situated a few millimeters from the bottom of the tank of the tray. The measuring wheel comprises a first portion (14) which is not very hydrophilic and which has a mean relative density of less than unity, and a second portion provided with hydrophilic means (13) that cause the unbalance of the wheel to vary as a function of the quantity of water retained in the hydrophilic means (13). The measuring device includes display means (15) for displaying the angular position of the measuring wheel (10), thereby providing an indication of the watering requirements of the medium.

The present invention relates to a device enabling the quantity of waterrequired for maintaining a proper moisture level in a cultivation mediumplaced in a tray to be determined by a direct reading.

The invention also relates to a plant tray specially adapted toimplement the device for determining the quantity of water required by acultivation medium placed in the tray.

In the prior art, the amount of water to be applied to a cultivationmedium and the frequency of watering are not obvious. Only a specialistcan determine the requirements of the medium merely from its appearanceand from its feel.

There exist plant pots having water reserves and including a device fordisplaying the water level in the bottom thereof. The main drawback ofthis type of plant tray is the time required to acclimatize a plant. Onaverage it takes two months for the roots to be able to draw water fromthe bottom of the tray. Traditional watering from above is essentialduring this period.

There also exist various types of apparatus whose operation is based ondetecting the moisture content of compost. Such apparatuses are complex,and are not suitable for domestic use. They are expensive due to thesophisticated design of apparatuses of this type, and they are intendedessentially for industrial growers.

Methods and devices that work by weighing are also known, such as thosedescribed in French patent document number 2 614 417, which for properoperation requires components that are strong, thereby giving rise to acost that is hardly compatible with generalized domestic usage. Inaddition, rating is required to take account of the water retentionpercentages of the mediums used for cultivation purposes. Such ratingrequires knowledge known only to the person skilled in the art.

The invention seeks to make it possible to indicate reliably thequantities of water that need to be applied to a plant tray in order tomaintain good growth while using a device that is simple, cheap, andconvenient to use.

Another object of the invention is to enable growing plants to be sold,in particular aromatic plants and flowering plants, and it relates toplant trays adapted to industrialized handling and to the requirementsof self-service distribution, and specially adapted to implementingdevices of the invention for displaying watering requirements.

These objects are achieved by a device for determining the quantity ofwater required by a cultivation medium placed in a tray, which device ischaracterized by the following points:

a) it comprises a measuring wheel disposed vertically and mounted on avertical partition so as to be free to rotate about a horizontal axis,while presenting an unbalance;

b) the bottom portion of the measuring wheel is situated a fewmillimeters from the bottom of the tank of the tray;

c) the measuring wheel comprises a first portion which is not veryhydrophilic and which has a mean relative density that is less thanunity, and a second portion provided with hydrophilic means which causethe unbalance of the wheel to change as a function of the quantity ofwater retained in the hydrophilic means; and

d) the measuring wheel is fitted with display means for displaying theangular position of the measuring wheel.

In a possible first embodiment, the unbalance of the measuring wheel iscreated by its horizontal axis being eccentric (e) relative to thegeometrical axis of the measuring wheel.

In a second embodiment, which may indeed be combined with the firstembodiment, the unbalance of the measuring wheel is created by anadditional mass applied to a localized peripheral region of themeasuring wheel.

In an embodiment that is particularly advantageous because it is simpleto implement, said first portion that is not very hydrophilic is made ofa lightweight material of density less than that of water, in the formof a disk in which a notch is formed, and in which said second portioncomprises a hydrophilic item constituted by sponge material fixed insaid notch by gluing.

Said second portion may extend over an angular sector lying in the rangeabout 30° to about 90°.

In a variant embodiment, the outside shape of the measuring wheel is notentirely circular, thereby defining a rocker having a first stableangular position when dry and angular positions different from the firstposition caused by a change in the center of gravity of the measuringwheel when said hydrophilic means are moist.

Advantageously, in this case, said first portion that is not veryhydrophilic is constituted in the form of a plate of lightweightmaterial whose density is less than that of water, and said secondportion comprises a hydrophilic item constituted by sponge materialfixed to a portion of the periphery of said plate over an angular sectorlying in the range about 45° to about 100° relative to the axis ofrotation of the measuring wheel.

According to a particular characteristic, the rocker-shaped measuringwheel selectively hides indications, marks, or pictograms formed on thepartition supporting the measuring wheel depending on its angularposition.

Said second portion may have a color different from that of said firstportion, thereby constituting said display means for displaying theangular position of the measuring wheel.

Said second portion may be disposed at least in part in the vicinity ofthe portion of the measuring wheel that is located at the top in theabsence of water in the tank of the tray, and is kept in a low positionwhen water is present.

In another possible embodiment, said first portion that is not veryhydrophilic is constituted by a waterproof compartment in the form of aportion of a disk, optionally containing a lining of lightweightmaterial, such that the mean relative density of said first portionremains less than unity.

According to a particular characteristic of the invention, said secondportion includes at least a few grains of water-retaining material whosevolume increases greatly in the presence of water.

The invention also provides a plant tray adapted to implementing adevice for determining the quantity of water required by a cultivationmedium, characterized in that it comprises a main compartment forreceiving the cultivation medium and plants to be cultivated, and anauxiliary compartment separated from the main compartment by a verticalpartition whose bottom portion allows water to pass therethrough andwhich supports a measuring wheel disposed vertically in the auxiliarycompartment, the measuring wheel being mounted on said verticalpartition in such a manner as to be able to rotate freely about ahorizontal axis while nevertheless having an unbalance, the bottomportion of the measuring wheel being situated a few millimeters from thebottom of the tank of the tray, the measuring wheel comprising a firstportion that is not very hydrophilic and that has a mean relativedensity less than unity, and a second portion provided with hydrophilicmeans causing the unbalance of the wheel to vary as a function of thequantity of water retained in the hydrophilic means, with the measuringwheel or the auxiliary compartment being fitted with display means fordisplaying the angular position of the measuring wheel.

According to the invention, determining and displaying the quantity ofwater required for watering the plants present in the plant tray is thusperformed simply by the hydrophilic portion of the measuring wheel. Thishydrophilic portion is placed in the same atmospheric conditions as thecultivation medium and its rate of evaporation varies in parallel withthat of the medium, with the drying out thereof changing the unbalanceof the measuring wheel and causing it to rotate, thereby making itpossible, e.g. by means of markers or symbols on the periphery of themeasuring wheel or by means of markers or symbols formed on thepartition supporting the measuring wheel and selectively hidden orrevealed by the measuring wheel, both to follow accurately and easilyany variations in the quantity of water that needs to be added toachieve the ideal degree of moisture for cultivation, and to top up thewater from time to time without applying too much water.

Other characteristics and advantages of the invention appear from thefollowing description of particular embodiments given by way ofnon-limiting example and with reference to the accompanying drawings, inwhich:

FIG. 1 is a perspective view of a plant tray of the invention fittedwith a device for determining water quantity constituting a firstembodiment of the invention;

FIGS. 2 and 3 are views along arrow F in FIG. 1 with the body of theplant tray removed, showing a first embodiment of a device fordetermining water quantity respectively in a water shortage position andin a water saturation position;

FIGS. 4 and 5 are diagrammatic section views respectively on line IV--IVof FIG. 5 and on line V--V of FIG. 4 showing a plant tray of theinvention fitted with a device for determining water quantityconstituting a second embodiment of the invention;

FIGS. 6 to 8 are front views of a measuring wheel as used in theembodiment of FIGS. 4 and 5, shown in positions correspondingrespectively to total water shortage, to partial water shortage, and towater saturation; and

FIGS. 9 and 10 are views analogous to FIGS. 2 and 3 showing a variantembodiment of the device for determining water quantity respectively ina water shortage position and in a water saturation position.

With reference initially to FIG. 1, there can be seen a plant tray 100which may be made of plastic and may be designed to be discarded afteruse or on the contrary to be reusable. The tray 100 has a bottom 101,side walls 102, and a top horizontal rim 103.

A preferably-removable partition 106 which may also be made of plasticdivides the inside volume of the tray 100 into a first compartment 21for receiving a medium for cultivating plants or flowers, and a secondcompartment 22 of smaller size for receiving a device for determiningthe quantity of water required by the cultivation medium placed in themain compartment 21.

For example, the partition 106 may be held in position by means ofvertical ribs 104 formed in the side walls of the tray 100. Thepartition 106 may also carry pegs 111 and 112 on its front face and maybe secured between ribs 104 formed on vertical walls 102 perpendicularto the partition 106 and the vertical wall of the tray 100 parallel tothe partition 106 and delimiting the compartment 22, with the pegs 111and 112 then acting as spacers. The partition 106 preferably includes aportion 108 which extends beyond the top rim 103 of the tray and whichprevents plants bearing against the device for measuring water quantity.

The partition 106 must not be completely water-tight, and for example itmay include openings or notches 7 in the vicinity of its bottom edge(FIGS. 2 and 3). The partition 106 may also rest on ribs formed in thebottom of the tray 100 and extending perpendicularly to the partition106.

A first example of the device for determining the quantity of waterrequired for maintaining proper moisture in the medium placed in themain compartment 21 of the tray 100 is now described with reference toFIGS. 1 to 3.

The device of the invention for determining the quantity of waterrequired essentially comprises a measuring wheel 10 mounted verticallyso as to be capable of rotating freely about a horizontal shaft 19 fixedon the vertical partition 106. Where appropriate, the height of theshaft 19 may be adjustable.

The measuring wheel 10 is positioned in the compartment 22 of the planttray 100 so that the bottom portion of the measuring wheel 10 is at adistance of a few millimeters from the bottom of the tank in the tray.The measuring wheel 10 is made so as to present an unbalance when drysuch that when dry it places itself in a predetermined angular positionsuch as that shown in FIGS. 1 and 2.

The measuring wheel 10 is essentially constituted by a first portion 14which is not very hydrophilic and having a mean density that is lessthan that of water, i.e. having a relative density of less than unity,and a second portion 13 which essentially comprises hydrophilic meansfor varying the unbalance of the measuring wheel 10 as a function of thequantity of water retained in the hydrophilic means.

More particularly, in the embodiment of FIGS. 1 to 3, the first portion14 is constituted by a disk made of a single piece of material that islighter than water and that is not very hydrophilic, e.g. such as cork,expanded polystyrene, or a cellular material such as a polyurethane foamhaving closed cells, for example. This first portion 14 in the form of adisk is pierced by an orifice 119 through which the horizontal supportshaft 19 passes. In addition, a notch 11 is formed in a portion of theperiphery of the disk 14 to enable the hydrophilic means 13 to beinserted, which means may be constituted in the simplest embodimentmerely by a piece of sponge material glued in the notch 11.

A small weight may be applied to the disk-shaped portion 14 that is notvery hydrophilic at a position that is on its side diametricallyopposite to the notch 11 about the shaft 19 so as to maintain themeasuring wheel 10 in its FIG. 1 position when dry, i.e. with its dryhydrophilic material 13 at the top. One or more marks 15 may be formedon the partition 106 to mark the angular position of the measuring wheel10. The portion 13 made of sponge material, such as polyurethane foamhaving open cells, for example, may itself be of a color or anappearance that is different from the body of the disk 14 so as tofacilitate marking the angular position of the measuring wheel relativeto the fixed marks 15.

In a variant, and in order to avoid using a weight, the measuring wheel10 may be mounted eccentrically as shown in FIGS. 2 and 3.

The orifice 119 of the disk 14 through which the horizontal shaft 19 maythus be offset by a distance e from the geometrical axis O of the disk14, thereby ensuring that the wheel 10 takes up the position shown inFIG. 2 with the hydrophilic material 13 at the top when the hydrophilicmaterial 13 is dry. When water is placed in the plant tray, the disk 14of lightweight material will tend to float on the water present in thebottom of the compartment 13, thereby attenuating its unbalance andcausing the measuring wheel 10 to rotate so as to bring its hydrophilicmaterial 13 into contact with the water. The hydrophilic material 13absorbs the water and the resulting increase in its weight keeps themeasuring wheel in the position shown in FIG. 3, i.e. with thehydrophilic material 13 at the bottom for so long as it remainssaturated with water. During evaporation of the water and theprogressive drying out of the hydrophilic means 13, which corresponds tothe cultivation medium drying out, the mass of the hydrophilic means 13will become smaller such that the measuring wheel will returnprogressively to the FIG. 2 position indicating that more water isrequired.

The hydrophilic means 13 may be adapted to the nature of the cultivationmedium and of the plants contained in the main compartment 21 of theplant tray. In particular, the volume of the sponge materialconstituting the hydrophilic means 13 may be adapted to differentconditions of use.

In addition, the hydrophilic means 13 may contain one or more grains ofa water-retaining material, for example, a polymer such aspolyacrilamide or a product obtained by culturing bacteria of thepolysaccharide family, with the water retainer having the property ofgreatly increasing in weight and in volume in the presence of water,which phenomenon is reversible.

It may be observed that the measuring device shown in FIGS. 1 to 3 canbe made in a manner that is extremely simple and cheap. Thus, a cylinderof lightweight material that is not very hydrophilic, such as cork orexpanded polystyrene for example, is easily perforated to make a channelforming an orifice 119, and then partially cut out to form alongitudinal notch 11. Sponge material optionally with a small quantityof water retainer may be fitted in the longitudinal notch, e.g. bygluing, to constitute the hydrophilic material 13. The resultingassembly is then merely sliced up to form a series of measuring wheels10 such as the wheels shown in FIGS. 1 to 3.

The partitions 106 are also easily mass produced in plastic, beingoptionally provided with notches or openings 7 in their bottom portions.Plastic studs 19, 111, and 112 may be fixed, e.g. by gluing, to eachpartition to constitute the shaft 19 that supports the measuring wheel10, and the spacers for positioning the partition 106 in the plant tray100.

The plant tray assembly 100 fitted with its measuring device may bedesigned to be discarded after use, given its low cost, however it couldalso be reusable since it constitutes an assembly that is relativelyrobust.

Numerous variants are possible.

Thus, FIGS. 9 and 10 show a measuring wheel 210 whose outside shape isnot entirely circular, thereby constituting a rocker which may bebootee-shaped, for example. Under such circumstances, the measuringwheel 210 is still unbalanced when dry, i.e. it is suspended from ahorizontal shaft 19 received in an orifice 219 that does not coincidewith the center of gravity of the measuring wheel, thereby defining afirst stable angular position (FIG. 9). This first angular positioncorresponds to water shortage and thus causes an indication to thiseffect to appear. The indication may be constituted by at least aportion of the hydrophilic means 213 reaching a high position, whichhydrophilic means may have a distinctive color, or else it may beconstituted by a mark on the edge of the measuring wheel, or indeed by areference symbol or pictogram 215a formed on the top portion 108 of thepartition 106 and uncovered by the measuring wheel 210 when in its dryposition. Thus, FIG. 9 shows a drawing 215a of a watering can indicatingthat the plants need watering.

When the hydrophilic means 213 is full of water, its weight increasesand it causes the rocker wheel 210 to take up the position shown in FIG.10 when saturated with water.

In the FIG. 10 position, the hydrophilic means 213 is in its bottommostposition and the water-shortage indication 215a is hidden by thelightweight and not very hydrophilic portion 214 of the wheel 210, whileanother indication 215b such as the message "OK" is revealed to indicatethat sufficient water is available. Naturally, various intermediatepositions are possible between the positions of FIGS. 9 and 10 when someof the water has evaporated but without the cultivation medium and thehydrophilic means 213 being completely dry.

The measuring wheel 210 may be made in the same way as for theembodiment of FIGS. 2 and 3 by means of a plate of lightweight materialof relative density less than unity for constituting the portion 214that is not very hydrophilic, and by a hydrophilic item 213 constitutedby sponge material fixed to the periphery of the plate 214.

The sponge material 213 is preferably disposed over an angular sectorcentered on the axis of rotation 119 and extending over a range of about45° to 100°. As can be seen in FIGS. 9 and 10, the hydrophilic item 213may be in the form of a sole placed at the bottom of the bootee-shapedplate 214. In the water-saturated position, the sponge material 213located near the bottom of the tray and full of water holds themeasuring wheel in the vertical position.

In contrast, in the dry position, the measuring wheel 210 returns to theprone position of FIG. 9, because of the reduction in the weight of thesponge material constituting the hydrophilic means 213. The hydrophilicmeans is then substantially vertical and when water is added, even invery small quantities, the "heel" of the sole-shaped hydrophilic means213 absorbs water which can rise by capillary causing the position ofthe measuring wheel 210 to change.

FIGS. 4 to 8 show a measuring wheel of the type that is somewhatdifferent from the measuring wheel 10 of FIGS. 1 to 3 or the measuringwheel 210 of FIGS. 9 and 10, even though it operates on a similarprinciple.

In the embodiment of FIGS. 4 to 8, the measuring wheel 1 has a firstcompartment 4 which may occupy between about 50% and about 75% of thevolume of the measuring wheel 1, and which constitutes a compartmenthaving a mean relative density of less than unity. The compartment 4 maybe empty and watertight, or it may be filled with a material that islightweight and impermeable, i.e. that is not very hydrophilic.

A weight constituting a counterweight may be disposed in localizedmanner in the bottom of the compartment 4 to establish an unbalance.

A second compartment 1a which occupies the volume left unoccupied by thefirst compartment 4 constitutes a supply that is not waterproof, inwhich a small quantity of water-retaining substance 3 such as thesubstances mentioned above is placed, e.g. in the vicinity of the weight2, which substance has small volume and low mass when dry such that themeasuring wheel 1 is then maintained in the position shown in FIG. 6because of the unbalance established by the weight 2. In the presence ofmoisture, the water retainer 3 increases considerably in volume and inweight and tends to occupy an ever increasing fraction of thecompartment 1a, thereby increasing the mean density of the compartment1a such that the unbalance of the measuring wheel 1 is changed, anddepending on the quantity of water present, the measuring wheel 1 isrotated about its shaft 9 fixed to the partition 6 of a plant tray 1which may be analogous to that described with reference to FIG. 1.

Visual indication means 5 are disposed on the periphery of the measuringwheel 1 so as to enable the angular position of the wheel 1 to beobserved, which angular position is a function of the quantity of watertaken into account by the water retainer 3.

FIG. 8 thus corresponds to water saturation, while FIG. 7 corresponds toa limited quantity of water being present, and FIG. 6 corresponds tototal absence of moisture.

When the water retainer 3 is dry (FIG. 6), the mass of the weight 2keeps the device 1 in a position which is marked by a top one of themarks 5. This mark 5 may advantageously be associated with an indicationof the volume of water that needs adding to the tray.

On coming into contact with water, the water retainer 3 increases inweight and in volume and causes the device to rotate (FIGS. 7 and 8).

When the water subsequently evaporates, the weight of the water retainer3 reduces and the device returns to its initial position (FIG. 6).

FIGS. 4 and 5 are sketches showing a tray 100 fitted with theabove-described embodiment of a device for determining a quantity ofwater.

The tray 100 is fitted with longitudinal ribs 107.

A moving partition 6 extends perpendicularly to the ribs and hasopenings 7 in its base, the top of the partition is terminated by acover for preventing the vegetation coming into contact with the movingwheel 1 of the device as supported by the horizontal shaft 9 supportedby the partition 6.

An opening 8 is formed through the top of the cover enabling theindications 5 written on the edge of the rotary wheel 1 of the device tobe read.

Inside the compartment 21, the space between the ribs 107 is filled witha substrate having a high water retention coefficient (e.g. vermiculite,peat).

The water retainer 3 has water retention characteristics similar to thatof the substrate placed in the compartment 21 and finds itself in thesame atmospheric conditions such that its rate of evaporation is similarand as a result the rotation of the measuring wheel 1 caused by thevarying unbalance generated by the water retainer 3 drying out enablesthe variations in the quantity of water that needs to be added toachieve ideal moisture in the plant tray 100 to be followed by means ofthe marks, thereby making the tray particularly well adapted to home usewith decorative or aromatic plants.

I claim:
 1. A device for determining the quantity of water required by acultivation medium placed in a tray (100), the device comprising ameasuring wheel (1; 10) disposed vertically and mounted on a verticalpartition (6; 106) so as to be free to rotate about a horizontal axis(9; 19), while presenting an unbalance, the bottom portion of themeasuring wheel (1; 10) being situated a few millimeters from the bottomof the tank of the tray, said measuring wheel comprising a first portion(4; 14) which is relatively unhydrophilic and which has a mean relativedensity that is less than unity, and a second portion provided withhydrophilic means (3; 13) which cause the unbalance of the wheel tochange as a function of the quantity of water retained in thehydrophilic means (3; 13), and wherein the measuring wheel (1; 10)includes display means (5; 15) for displaying the angular position ofthe measuring wheel (1; 10).
 2. A device according to claim 1, whereinthe unbalance of the measuring wheel (10) is created by the horizontalaxis (19) being disposed eccentric (e) relative to the geometrical axis(0) of the measuring wheel (10).
 3. A device according to claim 1wherein the unbalance of the measuring wheel (1) is created by anadditional mass (2) applied to a localized peripheral region of themeasuring wheel (1).
 4. A device according to claim 1 wherein said firstportion (14) that is relatively unhydrophilic is made of a lightweightmaterial of density less than that of water, and in the form of a diskin which a notch (11) is formed, and in which said second portion (13)comprises a hydrophilic element constituted by sponge material fixed insaid notch (11) by adhesive.
 5. A device according to claim 1, whereinsaid second portion (13) extends over an angular sector lying the rangeabout 30° to about 90° .
 6. A device according to claim 1 wherein theoutside shape of the measuring wheel (210) is not entirely circular,thereby defining a rocker having a first stable angular position whendry and angular positions different from the first position caused by achange in the center of gravity of the measuring wheel (210) when saidhydrophilic means (213) are moist.
 7. A device according to-claim 6,wherein said first portion (214) that is relatively unhydrophiliccomprises a plate of lightweight material whose density is less thanthat of water, and in that said second portion (213) comprises ahydrophilic element constituted by sponge material fixed to a portion ofthe periphery of said plate (214) over an angular sector lying in therange about 45° to about 100° relative to the axis of rotation (19) ofthe measuring wheel (210).
 8. A device according to claim 6, saidpartition bearing indicia and wherein the rocker-shaped measuring wheel(210) includes means for selectively hiding said indicia, depending onits angular position.
 9. A device according to claim 4 wherein saidsecond portion (13; 213) has a color different from that of said firstportion (14; 214), thereby constituting said display means fordisplaying the angular position of the measuring wheel (10; 210).
 10. Adevice according to claim 1 wherein said first portion (14) that isrelatively unhydrophilic comprises a waterproof compartment in the formof a portion of a disk, such that the mean relative density of saidfirst portion (14) remains less than unity.
 11. A device according toclaim 1 wherein said second portion (3; 13) includes at least a fewgrains of water-retaining material whose volume increases greatly in thepresence of water.
 12. A device according to claim 1 wherein said secondportion (3; 13; 213) is disposed at least in part in the vicinity of theportion of the measuring wheel (1; 10; 210) that is located at the topin the absence of water in the tank of the tray, and is kept in a lowposition when water is present.
 13. A device according to claim 1wherein the bottom portion of the partition (6; 106) supporting themeasuring wheel is provided with orifices or notches (7) allowing waterto pass.
 14. A plant tray adapted to implement a device for determiningthe quantity of water required by a cultivation medium, said traycomprising a main compartment (21) for receiving the cultivation mediumand plants to be cultivated, and an auxiliary compartment (22) separatedfrom the main compartment (21) by a vertical partition (6; 106) whosebottom portion allows water to pass therethrough and which supports ameasuring wheel (1; 10) disposed vertically in the auxiliary compartment(22), the measuring wheel being mounted on said vertical partition insuch a manner as to be able to rotate freely about a horizontal axiswhile nevertheless having an unbalance, the bottom portion of themeasuring wheel (1; 10) being situated a few millimeters from the bottomof the tank of the tray, the measuring wheel comprising a first portion(4; 14) that is relatively unhydrophilic and that has a mean relativedensity less than unity, and a second portion provided with hydrophilicmeans (3; 13) causing the unbalance of the wheel to vary as a functionof the quantity of water retained in the hydrophilic means (3; 13), withthe measuring wheel (1; 10) or the auxiliary compartment (22) includingdisplay means (5; 15) for displaying the angular position of themeasuring wheel (1; 10).
 15. A plant tray according to claim 14, whereinthe tray includes ribbed walls and wherein the vertical partition (6;106) is removable and co-operates with the ribs (104) of the walls ofthe tray.
 16. A plant tray according to claim 14 wherein said tray ismade of plastic.
 17. A device according to claim 10, wherein saidwaterproof compartment contains a lining of lightweight material.